The present invention is directed to an apparatus and method for detecting and measuring a secondary material that has been deposited at intermittent intervals onto a moving substrate. More particularly, the apparatus and method of the present invention employs at least one x-ray emitter located on a first side of the moving substrate, and at least one x-ray detector located on the opposite side of the moving substrate.
Various devices exist for measuring the thickness of materials, including moving materials. Contact gauges and similar other measurement devices that require physical communication with the material to be measured have been known for many years. More recently, non-contact measurement devices have been developed that allow for the measurement of various characteristics of a moving material sample, without the need for physical communication between the material and the device. These devices may include, for example, a source of radiation and a means to detect the source of radiation after it interacts with the moving material sample.
A number of these non-contact measurement devices were developed for use in the manufacturing of sheet (roll) steel. These devices have been used to measure thickness, or slight variations in thickness that may occur over the unrolled length of a steel coil. Such devices have also been used in the paper manufacturing industry to measure, for example, the typical basis weight or moisture content of a moving paper web. These devices have further been used to measure the thickness of a coating or film that has been deposited onto the surface of a moving sheet of material. For example, the devices may be used to measure the average coating thickness across a painted or treated sheet of metal, or to measure the thickness of a protective (aseptic) coating layer deposited on to the moving stock for a food or beverage carton. Thus, typically, such devices have been used to measure a dimension or characteristic that is substantially constant, or that varies only slightly and over a considerable period of time. Many of these known devices operate by measuring reflected (back-scattered) radiation.
It is also desirable, however, to be able to detect and measure a secondary (additive) material that is deposited onto a moving substrate intermittently, rather than substantially uniformly across its surface. For example, in certain manufacturing processes, it may be necessary or desirable to deposit or apply an additive to a moving substrate in a manner that produces only intermittent, repetitive regions of the additive. Most commonly, such regions would extend across the width of the moving substrate. The regions may be deposited at regular or irregular intervals onto the substrate.
One particular such process of interest involves the treatment of a moving web of a paper substrate that will eventually be used to produce cigarettes or other similar smoking articles. As the moving paper web is expelled from a paper-making machine or other manufacturing or treatment device, one or more additives may be periodically deposited thereon. More particularly, for example, intermittent regions (bands) of a self-extinguishing additive or some other material may be deposited in rows that extend substantially across the width of the paper substrate. Such periodic additive deposits may be used, for example, to produce a modification of the burn characteristics of a cigarette or other smoking article that is later produced from the paper substrate. More specifically, the additive(s) may be selected and deposited in such a manner that a smoking article produced from the paper web will have reduced static burn characteristics, or may be entirely self-extinguishing when left in a static condition for a certain period of time.
In order to achieve such a desired end result, it is generally necessary to carefully control how the secondary material is deposited onto the substrate. For example, aside from ensuring that the secondary material is deposited onto the substrate at the location or interval desired, it is also typically required to precisely control the amount of secondary material that is deposited. For purposes of further illustration, and not limitation, it is known that in the exemplary process described above, wherein a self-extinguishing additive is deposited at repeating intervals to a moving web of smoking article paper, the amount of deposited self-extinguishing additive must be carefully monitored and controlled. More specifically, it has been found that the self-extinguishing additive must be deposited onto the paper substrate within a narrow thickness range in order to produce the desired static self-extinguishing characteristic without also causing the smoking article to self-extinguish while being smoked.
Thus, as can be seen from the foregoing discussion, there exists a need for a method of detecting and measuring a secondary material that is deposited onto a moving substrate at regular or irregular intervals. Such a method must be capable of accurately determining whether the secondary material deposits are within an acceptable thickness range, even when the thickness of such deposits is minimal. Such an apparatus must further be capable of accurately detecting and measuring substantially narrow regions or bands of the secondary material. Additionally, because the velocity of the moving substrate may be substantial, and the width of the secondary material deposits may be minimal, such a method must be capable of rapid measurement.
The method of the present invention satisfies this need. The method of the present invention preferably employs one or more X-ray apparatuses, each of which includes a preferably non-nucleonic x-ray emitter(s) and one or more corresponding x-ray detectors. Preferably, the x-ray emitter is located on one side of a moving substrate having known X-ray absorption characteristics, and is oriented to direct an x-ray beam at the moving substrate. The x-ray detector is preferably located on the opposite side of the moving substrate, and is located to receive an amount of the x-ray beam that passes through (is transmitted by) the moving substrate. The amount of the x-ray energy that is transmitted (or absorbed) by areas of bare substrate can be measured. The present invention is also able to measure the amount of the x-ray energy that is transmitted or absorbed by areas of the substrate containing a secondary material deposit. The difference in measurements of absorbed x-ray energy can be used to determine whether an acceptable amount of secondary material is present. By referencing known x-ray absorption properties of the substrate and/or additive materials, the measurements can be used to determine and report thickness, density or other material characteristics, if desired. Measurements can be reported in a variety of formats, such as, for example, whether the secondary material deposit is acceptable or unacceptable, or as an output of density, total thickness, secondary material thickness, or as a percentage thickness increase. The method of the present invention may also account for the fact that the substrate itself may not be of equal thickness across the whole of its length.